K. T. Poroshin et al., Chemical Abstracts, 53 21693h, described the use of carbobenzoxy-L-prolylglycyl-L-proline as an intermediate to prepare L-prolylglycyl-L-proline, however, this reference described neither the essential N-carboxyalkyl substituent nor the critical mid-unit both of which characterize the structures of these new compounds. Poroshin, also, described no biological activity for any of the compounds he prepared. The compounds of this invention, therefore, differ from those in the prior art by two structural parameters.
EPO application No. 12,401 describes certain carboxyalkyl dipeptides which are angiotensin converting enzyme inhibitors. The EPO compounds differ from those of the present invention in mechanism of action as well as in chemical structure. The N-carboxyalkyl substituents are not substituted on the prolyl unit of the EPO dipeptides.